The Preservation filming process includes a Master Negative, Silver Duplicate Negative and Silver Positive Service Copy. We will attempt to outline these different types of film as well as microfilm standards in this article.
Advantage Preservation microfilms Historical Newspapers and other documents on a 35 mm Silver Halide film to meet or exceed all ANSI and AIIMS specifications, ensuring over 500 years of protection! Silver film is the only type recognized for preservation or “archival” purposes. The image is captured by exposing silver compounds to light. Wet-processed silver film is the only type that can be recognized as archival, as dry silver film is not fixed by chemical processing and washing. This photographic film containing photosensitive compounds suspended in a suitable material. When developed, the image consists of metallic silver. The image is produced by exposing light-sensitive silver compounds in a film emulsion to light.
The original, or Master silver-gelatin microfilm is always a negative image, but positive or negative duplicates can be made. The Master Negative is also known as the “first generation film” and is an image produced directly from a subject or original document. This is the archival copy, which is used to produce a duplicate negative for the generation of use copies. The only subsequent use of the master negative should be the reproduction of a duplicate negative lost to damage or disaster.
The Silver Duplicate Negative is used to generate use copies or service copies for the collection. The Duplicate Negative is the “second generation film” and needs to be stored under the best available conditions, since it serves as a working master, to protect the master negative.
The Silver Positive Service copy is the third and final generation of the film and produced for public use such as with a microfilm reader.
Our customers receive a silver halide positive or negative duplicate microfilm, depending on their preference. We also store a copy of the microfilm reels in our purpose built humidity and temperature controlled vault.
With our filming process customers can expect a fast turnaround time for microfilm, in most cases taking no longer than 30 days for us to complete the project and return the film.
After outlining our process it’s also important to acknowledge other terms and types of film that are common in the industry.
Roll Film or roll microfilm, can be found in both 16mm and 35mm width and is typically 100 ft in length. In addition to Silver-Gelatin, Diazo film and Vesicular film are other common types of microfilm.
Diazo Microfilm is used to create user copies of master microfilm, micrographic or microform. Diazo refers to the diazonium salts used in the coating layer of this microfilm. The salts are combined with dyes to produce the image. This is a slow print film, which, after exposure to light that is strong in the blue to ultraviolet spectrum and after development, forms an image. Diazo film generally produces non reversible images, i.e., a positive image will produce a positive image and a negative image will produce a negative image.
The word vesicular in Vesicular Microfilm derives from vesicles, or bubbles that form when an image is developed through heating, which causes nitrogen from diazonium salts to expand. Ultraviolet is then used to decay the salts. Pressure on the film can damage the image-bearing bubbles, and faulty processing can cause the bubbles to burst, resulting in damage to the image. This a film in which the light-sensitive component is suspended in a plastic layer. On exposure the component creates optical vesicles – bubbles in the layer. These imperfections form the latent image. The latent image becomes visual and permanent by heating the plastic layer and then allowing it to cool. Vesicular film has a grey color in appearance. When placed in a viewer it provides a positive image to the eye. Vesicular duplicating film is a reversing film e.g. a negative master provides a positive duplicate.
While related technologies such as digitization provide accessibility, microfilm has remained the standard as the only true preservation method. At Advantage Preservation, we continue our mission of preserving historical content on microfilm, and developing digital tools to allow for access to that content!